Conventionally, in a tire mounted on a vehicle such as a passenger vehicle, various methods have been used to reduce tire noise generated when the tire rolls on a road surface having irregular recesses and bumps, such as a paved road with a rough road surface. For example, there is known a tire using rubber with high stiffness in the shoulder portion of a tread (refer to Patent Literature 1). According to such a tire, deformation of the tread can be suppressed when the bumps, of the recesses and bumps of the road surface, wedge into the tread. Due to this, the increase of the contact pressure of the tread is suppressed, and the increase of tire noise when the tire rolls on a rough road surface can be suppressed.
Incidentally, nowadays, as a result of progress in the intensive study on the mechanism of tire noise generated, it has been made clear that the vibration of the buttress portion due to recesses and bumps of the road surface is also a cause of tire noise. In other words, when the road surface is smooth, normally, the buttress portion does not contact the road surface. On the other hand, when there are small recesses and bumps on the road surface, such as a paved road with a rough road surface, the buttress portion does contact the road surface, and due to these recesses and bumps, the buttress portion vibrates. Vibration of the buttress portion like this increases tire noise. In order to suppress the generation of such tire noise, it is considered to form small recessed portions on the buttress portion. However, there is a problem that, when such small recessed portions are formed on the buttress portion that is severely deformed, cracks originating from the recessed portions easily progress.